A trio of theorists, including one from the National Institute of Standards and Technology (NIST), have described how a future quantum computer could be used to simulate complex, high-energy collisions of subatomic particles. Given a working quantum computer—still under development—the algorithm could solve important physics problems well beyond the reach of even the most powerful conventional supercomputers.

High-energy particle collisions represent one of the most important frontiers of modern physics, but the interactions involved are so complex they often cannot be calculated from existing models. It's an experimental science, and one that requires big experiments like the multibillion euro Large Hadron Collider (LHC).

Modeling such collisions would not be beyond a quantum computer, however. Also the focus of intense research, such machines will take advantage of quantum mechanics—the laws that govern the interaction of subatomic particles. These laws allow quantum switches to exist in both on and off states simultaneously, so they will be able to consider all possible solutions to a problem at once.

"We have this theoretical model of the quantum computer, and one of the big questions is, what physical processes that occur in nature can that model represent efficiently?" said NIST theorist Stephen Jordan. "Maybe particle collisions, maybe the early universe after the Big Bang? Can we use a quantum computer to simulate them and tell us what to expect?"

Questions like these involve tracking the interaction of many different elements, a situation that rapidly becomes too complicated for today's most powerful computers.

The team developed an algorithm—a series of instructions that can be run repeatedly—that could run on any functioning quantum computer, regardless of the specific technology that will eventually be used to build it. The algorithm would simulate all the possible interactions between two elementary particles colliding with each other, something that currently requires years of effort and a large accelerator to study.

A substantial amount of the work on the algorithm was done at the California Institute of Technology, while Jordan was a postdoctoral fellow. His co-authors are fellow postdoc Keith S.M. Lee (now a postdoc at the University of Pittsburgh) and Caltech's John Preskill, the Richard P. Feynman Professor of Theoretical Physics.

"We believe this work could apply to the entire standard model of physics," Jordan says. "It could allow quantum computers to serve as a sort of wind tunnel for testing ideas that often require accelerators today."